Invoker + Legion Commander

Why this works

Winning a Duel is much easier when your target is also getting hit by a Sun Strike. Legion Commander's goal is to isolate and eliminate a key enemy, but she can sometimes lack the damage to finish the job herself. Invoker provides the perfect solution with his global burst, turning any Duel into a near-certain kill. The setup is also incredibly strong; a Tornado can lift a hero out of position, allowing Legion to walk in and start the Duel uncontested. Spells like Cold Snap can even add more lockdown inside the Duel, ensuring the target can't fight back.

This partnership allows Legion Commander to start snowballing with Duel victories much earlier and more reliably than she normally could. The threat of a global gank forces opponents to play passively and group up, ceding map control. To counter this, the other team needs heroes with strong save abilities to protect the Dueled target. Without that, Invoker and Legion can systematically pick off heroes, build an insurmountable lead, and then use Invoker's teamfight control to secure objectives and close out the game.